At its root, the word “astrobiology” means “biology of the stars.” It is the branch of science that concerns the origin and evolution of life on Earth – the only place that, at present, we are certain life exists – and the potential for life to be distributed across the Universe. In this chapter, we explore the evolutionary relationships of life on Earth and review the necessary ingredients and permissible environmental conditions for the origin and evolution of life. We also discuss the characteristics of early life on Earth, and the physical and geochemical evidence for life that might be used to target habitable environments – and potentially to detect evidence of life – elsewhere in the Universe.

All planets, and many moons and asteroids, have experienced igneous activity. Magma compositions on Earth vary widely, reflecting different melting mechanisms in the various tectonic settings, different source compositions, and the effects of magmatic processes like fractional crystallization and assimilation. Most magmas are emplaced in plutons rather than erupt on the surface. On other planets, we study volcanic constructs and rocks, because plutonic rocks are not commonly exposed. Eruptive styles vary with each planet, depending on neutral buoyancy zones in the subsurface, the amount of volatiles in magmas, gravity, atmospheric pressure, and other factors. Basalts are ubiquitous on all rocky bodies, and fractional crystallization of basaltic magmas has produced cumulates and fractionated residual melts. The formation of abundant, highly evolved felsic magmas, as far as we can presently discern, has been restricted to Earth. On some icy bodies cryovolcanoes erupt cold brines and gases. Volcanism mostly ceased on the Moon when melting retreated to the deep interior, on Mercury when global contraction closed pathways for magma ascent, and on asteroid Vesta when the radiogenic heat sources were exhausted. Magmatic activity continues on Earth and Io, and recent (possibly ongoing) activity occurs on Venus and Mars. Where sufficient information is available to judge, magma compositions appear to have evolved with time, in a manner unique to each body.

The previous three chapters cover the elastic behaviour of composites containing aligned fibres that are, in effect, infinitely long. Use of short fibres (or equiaxed particles) creates scope for using a wider range of reinforcements and more versatile processing and forming routes (see Chapter 15). There is thus interest in understanding the distribution of stresses and strains within such composites, and the consequences of this for the stiffness and other mechanical properties. In this chapter, brief outlines are given of two analytical models. In the shear lag treatment, a cylindrical (short fibre) reinforcement is assumed, with stress fields in fibre and matrix being simplified (leading to some straightforward analytical expressions). It introduces important concepts concerning load transfer mechanisms, although it is not very widely used for property prediction. The Eshelby method, on the other hand, is based on the reinforcement being ellipsoidal (anything from a sphere to a cylinder or a plate): the analysis is more rigorous, but with the penalty of greater mathematical complexity. The model is only briefly described here. Its use also introduces an important concept – that of a misfit strain, which is helpful in areas well beyond those of the mechanics of conventional composite materials.

We describe the flow of liquids – water in the inner Solar System, hydrocarbons on Saturn’s moon Titan – and its effects on planetary surfaces. Liquids fall onto, flow through, and emerge from planetary landscapes. The resultant entrainment, transport, and deposition of sediment are observed in a variety of forms, which can be ascribed to the variety of surficial and subsurface flow conditions. As the area within the highest topographic elevations surrounding a river network, the drainage basin provides a natural hydrologic unit for defining and discussing these various processes. In cratered landscapes on Mars and Titan, drainage divides are often obscured by impact craters and by atmospheric degradation, although in younger terrains the crater rims themselves often demarcate the drainage divides. River networks exhibit morphologies based on surface and subsurface controls on the flow. Whereas networks on Earth are primarily dendritic (branching in a tree-like fashion), the majority of network morphologies on Titan are rectangular, suggesting tectonic influence. Deposits from channelized flow provide data on the flow conditions and sediment load. Fans on Mars and Titan provide evidence of subaerial deposition. Deltaic deposits on those bodies, along with possible shorelines and inferred tsunami deposits around the northern lowlands of Mars, imply deposition and erosion in lakes, seas, and perhaps even a vast martian ocean. Fluvial, alluvial, and lacustrine landforms thereby provide insights into climate, surface, and sedimentologic processes on planetary bodies.

In the previous chapter, it was shown that an aligned composite is usually stiff along the fibre axis, but much more compliant in the transverse directions. Sometimes, this is all that is required. For example, in a slender beam, such as a fishing rod, the loading is often predominantly axial and transverse or shear stiffness are not important. However, there are many applications in which loading is distributed within a plane: these range from panels of various types to cylindrical pressure vessels. Equal stiffness in all directions within a plane can be produced using a planar random assembly of fibres. This is the basis of chopped-strand mat. However, demanding applications require material with higher fibre volume fractions than can readily be achieved in a planar random (or woven) array. The approach adopted is to stack and bond together a sequence of thin ‘plies’ or ‘laminae’, each composed of long fibres aligned in a single direction, into a laminate. It is important to be able to predict how such a construction responds to an applied load. In this chapter, attention is concentrated on the stress distributions that are created and the elastic deformations that result. This involves consideration of how a single lamina deforms on loading at an arbitrary angle to the fibre direction. A summary is given first of some matrix algebra and analysis tools used in elasticity theory.